Various types of machines have been developed for measuring the uniformity of a tire, including the tire's radial runout, i.e., or out of roundness. Many of these machines are configured for laboratory settings, while others are intended for field use. An example of the latter type of machine is disclosed in U.S. Pat. No. 5,448,910. This machine can be transported, for example, to an automotive production plant where a finished vehicle is being tested and vibration is detected. The tire/wheel assembly can then be tested to determine if the vibration causing problem resides in the tire/wheel assembly. This avoids the need to ship the tire/wheel assembly to a remote laboratory for testing, which is time consuming.
For several reasons it would be advantageous to have a test apparatus that can measure tire uniformity and particularly radial runout while the tire/wheel assembly remains mounted to the vehicle. For instance, this would enable detection of a runout problem arising from the wheel-hub interface. Also, this eliminates the need to remove the tire/wheel assembly from the vehicle and install it on a test machine. Moreover, it would be advantageous for such test apparatus to be of small size and weight for easy portability, and particularly of a size and weight which allows the test apparatus to be hand carried from one location to another.